Hydraulically operated surfacegrinding machine



sept. 5, 192.9. A, G. BELDEN HAL HYDRAULICALLY OPERATED SURFACE-GRINDINGMACHIN 20, 1938 5 Sheets-Sheet l Filed Aug.

FILEJERT BEELDEN CFIHL E. F'LYGHHE I @Mmeaxm' Sept. 5, 1939. 2,171,519

HYDRAULICALLYOPERATED SURFACE-'GRINDING MACHINE A. G. BELDEN ET A1.

Filed Aug. 20, 1938 3 Sheets-Sheet 2 3mm/vbo@ HLEERTEEELDEN CHRI. GFLYEHRE Sept.- 5, 1939- A. G. BELDEN ET AL.

HYDRAULICALLY OPERATED SURFACE-GRINDING MACHINE l 20, 1938 5SheeS-Sheefl 3 Filed Aug.

EHRLGF'LYGHHE m" www Patented Sept. 5, 1939 UNITED STATES PATENT OFFICEHYDRAULICALLY OPERATED SURFACE- GRINDING MACHINE Application August 20,1938, Serial No. 225,978

9 Claims.

'Ihe invention relates to grinding machines, and more particularly to asurface grinding machine for grinding plane surfaces on a work piece.

One object of the invention is to provide a surface grinding machinewith an electrically controlled transverse feeding movement for thegrinding wheel. Another object of the invention is to provide a surfacegrinding machine with a hydraulically actuated electrically controlledtransverse feeding. movement for the grinding wheel. A further object ofthe invention is to provide a hydraulically operated surface grindingmachine with a tandem fluid pump one of which serves to feed thegrinding wheel transversely during the period of reversal at the end ofthe table stroke and both of which serve to traverse the work tableduring the grinding stroke.

A further object of the invention is to provide a hydraulicallyoperatedtransverse grinding wheel feeding mechanism with an electricallycontrolled time delay mechanism to regulate the extent of transversefeed of the wheel. Another object of the invention is to provide ahydraulic counterbalance for the vertical slide to facilitate manualvertical adjustment of the grinding wheel. A further object of theinvention is to provide a power operated vertical positioning mechanismfor positioning the grinding wheel. Other objects will be in partobvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts, as will beexemplified in the structure to be hereinafter described, and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawings, in which is shown one of various possibleembodiments of the mechanical features of this invention,

Fig..1 is a front elevation of the improved surface grinding machine;

Fig. 2 is a plan view of the improved surface grinding machine, on aslightly reduced scale;

Fig. r3 is a fragmentary detail .view of the power operated verticalfeeding mechanism and the hydraulic counterblance; and

Fig. 4 is a diagrammatic illustration of the hydraulic system and theelectrical wiring diagram for the automatic cross feed.

A surface grinding machine has been illustrated in the drawings having abase l which supports a longitudinally reciprocable work table I l onthe usual V-way andv at way (not shown). A grinding wheel l5 isrotatably mounted on a transprise a manually operable feed wheel which10 is mounted on the outer end of a shaft 2| which is journalled inbearings (not shown) in the base I0. The shaft 2| supports a worm 22which. meshes with a worm gear 23. The worm gear 23 is provided with acentral aperture which is threaded to mesh with a feed screw 24. Theupper end of the feed screw 24 is connected to a lug 25 projecting fromthe vertically movable slide Il. A pair of'nuts 26 and 2l serve rigidlyto secure the screw 24 to the lug 25. The worm gear 23 `is rotatablysupported in housing 32, which is fixed relative to the base I0, so asrotatably to support the worm gear 23 and hold it against endwisemovement so that when the gear 22 is rotated, the threaded aperturemeshing with the feed screw 24 will produce an endwise vertical movementof the screw 24 together with the vertical slde Il, the wheel slide I6and the grinding wheel I5.

Table reciprocating mechanism The table Il is arranged so that it may bereciprocated by a power operated mechanism to pass the work piecebeneath the operative face of the grinding wheel'l5. In the preferredform, the reciprocating mechanism comprises a fluid pres' sure'systemcomprising a cylinder 35 which is xedly mounted by means of brackets 36and 3l to the under side of the table Il. A pair of spaced pistons 33and 39 are slidably mounted within the cylinder 35 and are connectedlwith the hollow piston rods 4U and 4I, respectively, which are in turnfixed at their outer ends to brackets 42 and 43, respectively. Thebrackets 42 and 43 are fixedly mounted on opposite ends of the base I0.

The base l0 is preferably of a hollow box-like construction forming auid reservoir 45, from which fluid is pumped by means of a iiuid pumpvthrough the pipe 49 enters through a port at the through a pipe 60 intoa valve chamber 5|, and out through a pipe 62 into the reservoir 45.

Throttle valve In order to control the speed of movement of l the tableduring grinding, it is desirable to provide a suitable throttling devicewhich in the preferred form comprises a throttle valve 65 preferablylocated within the exhaust pipe line 62 whereby the exhaust of fluidfrom the system is throttled to regulate the speed of movement of thetable. This valve has been illustrated diagrammatically as a rotary typethrottle valve (Fig. 4). A control lever 66 is provided for actuatingthe throttle valve to regulate the speed of movement of the table or toclose the valve to stopthe table movement when desired.

A second fluid motor 10 preferably arranged in tandem with the fluidpump 46 and driven 'by the motor 41 is provided for actuating thetransverse or cross feeding movement of the grinding Wheel |5 whichoccurs during the reversal movement of the work table Il. During thenormal grinding stroke of the table I, the pressure from the pump 10 isutilized to supplement uid under pressure from the pump 46 so as todrive the work table at a higher rate of speed. The pump 10 forces fluidthrough a. pipe 1| and a pipe 12 to the grinding wheel cross feedingmechanism to be hereinafter described.

Fluid under pressure from the pipe 12 may also pass through a pipe 13 toa control valve 14 which is connected to operate in timed relation withthe reverse valve 50. The valve 14 is vprei"- erably a piston type valvecomprising a valve stem 15 having formed integrally therewith aplurality of valve pistons 16, 11 and 18. In the position of the valveshown in Fig. 4,'rluid under pressure from the pump 10 passing throughthe pipe 13 enters a valve chamber 19 located be'- tween the valvepistonsv 11 and 18 and is forced out through a pipe which is connectedwith the pipe 49 so that fluid under pressure from the pump 10 is forcedthrough the pipe 49 to the table reversing valve 50 to aid the pump 46in driving the table at a rapid rate. The valve'stem 15 is connected bya stud 8| with the lower end .of alever 82 which is actuated at reversalto cut olf the pipe'80 and thereby force all of the fluid from the pump10 through pipe 12 for a denite interval during the shifting of thevalve 50 into its reverse position. Y v

Transverse movement-grinding wheel 'I'he grinding wheel I5 and itssupporting slide I6 are arranged so that they may be moved transverselyby a manually operable mechanism including a manually operable handwheel 85 mounted on the outer end of the shaft 86 which is operativelyconnected through. a gear mechanismto move a rack bar 81 endwisel..V Therack bar 81 is preferably fixed to the upper surface of the wheel slideI6 and serves to move the slide I6 and grinding Wheel I5 in eitherdirection according to the rotation of the manually operable wheel 85.The manually operable feeding mechanism has not been illustrated indetail in the present application. This mechanism is substantiallyidentical to that shown in the prior patent to Flygare et al. No.2,022,542 dated November 26, 1935, towhich reference may be had fordetails of disclosure not found herein.

A power operated mechanism isv also provided for moving the grindingwheel slide I6 and the grinding wheel I 5 transversely at the ends ofthe table stroke so that on successive reciprocations of the workbeneath the wheel I5, the wheel will grind a different overlapping pathon the Work piece. In the preferred construction, a rotary fluid motor90 is mounted on the vertical slide I1. This motor is a vane type motorhaving a single vane 9| mounted on a rotor shaft 92. The shaft 92 alsocarries a gear 93 meshing with a pinion 94 which in turn meshes with therack bar 81 carried .by the wheel slide I6. A control or reversing valve95 is provided to control the admission of fluid and the exhaust offluid from the motor 90. The reversing valve 95 is of the piston typecomprising a valve stem 96 having a plurality of valve pistons formedintegrally therewith. Fluid under pressure passing through the pipe 12passes through a pipe 91, a portion of which is preferably eitherflexible or telescopic, to a valve chamber 98 and passes out into amotor chamber 99 to cause the vane 9| to move in a counterclockwisedirection (Fig. 4) which serves through the gear 93 and pinion 94 tomove the rack bar 81 and wheel slide I6 toward the left (Fig. 4). Duringthis movement fluid under pressure exhausts from a motor chamber |00through a valve chamber I 0|y and a pipe |02 which exhausts into thereservoir 45.

A manually operable knob |95 is mounted on the outer end of the valvestem 9B and serves to facilitate manual shifting of the reversing valve95.' A solenoid operated valve I 03 connected in the pipe line |02 andactuated by a solenoid |04 is normally closed and thereby serves toprevent movement'of the fluid within the wheel traverse system so as tohold the wheel slide I6 and grinding wheel I5 against transversemovement. The valve |03 is merely a shut-off valve and does not serve inany way to throttle the fluid when A throttle valve, preferably a needletype valve |06, is actuated by a manually operable knob |01 and servesto regulate the exhaust of-fluid from the system above described tocontrol the normal rate of transverse feeding movement of the grindingwheel as it is indexed transversely.

In order to facilitate truing of the grinding wheel, itis desirable toprovide a truing speed valve which is independent of the normal speedcontrol valve whereby the wheel may be coritinuously traversed at a slowtruing speed without disturbing the normal speed adjustment of thetransverse movement of the grinding wheel. This is preferablyaccomplished by providing a second needle valve |10 which may be readilyadjusted to throttle the exhaust of lluid from the motor 90 to producethe desired truing speed, 'and the valve is arranged so that it may bereadily shifted to and from an operating position by means of a knob Iso that during the normal operation of the machine, the valve IID isrendered inoperative and the valve |96 serves to control the eX- haustof fluid from the system.

Wheel slide' reversing mechanism in timed relation with the transversemovement of the wheel slide I0. A pair of adjustable dogs |20 and |2|are supported on a bar |22 carried by the wheel slide I6. The dogs |20and |2| are arranged to engage a reversing lever |23 which isoperatively connected to shift the valve stem 96 in an endwise directionto reverse the direction of movement of the wheel after it has traversedtransversely through a predetermined distance to cover the width of thework piece being ground. A load and fire spring-pressed plunger (notshown) is contained within a casing |20 and serves normally to snap thereversing lever from one position to the other when 4actuated by thewheel slide dogs |20 and |2|.

This reversing mechanism has only been illustrated diagrammatically inFig. 4. This reversing mechanism is identical with that shown in theprior patent to Flygare and Wood No. 2,022,542 dated November 26, 1935,to which reference may be had for details of disclosure not foundherein;

Table reversing lever A reversing lever |30 is pivotally mounted on thefront of the machine base and is operatively connected to shift thereversing valve 50 in timed relation with the longitudinal movement ofthe table to reverse the direction of movement of the same after it hastraversed a predetermined distance. A pair of adjustable dogs i3! and|32 mounted on the front edge of the table serve to engage the reverselever and to shift the lever and the reversing valve 50 to change thedirection of flow of fluid to the cylinder 35. A load and fire mechanism(not shown) is provided to aid in shifting the valve 50 into its reverseposition. This has not been illustratedinfdetail' in the present casesince it is identical with that shown in the above mentioned priorpatent tol Fiygare and Wood No. 2,022,542 dated November 26, 1935, towhich reference may be had for details of disclosure not found herein.

Automatic grinding wheel cross feed The shut-off valve |03 abovedescribed is normally closed and is arranged to be opened by means ofthe solenoid |04. The valve |03 is maintained in a closed positionduring the longitudinal reciprocatory movement of the work table so asto hold the grinding wheel l5 against transverse movement. The valve |03is opened during the period of reversal of the table to feed the wheell5 transversely for grinding a new path on the work piece mounted on thetable and closing of the solenoid valve |03 in timed relation with thereversing mechanism of the table A normally open limit switch |35 ismounted on the reversing lever |30 and is provided with an actuatingroller |36 which is arranged in the path of the table dogs |30 and I3|.When either of the table dogs |3| or |32 engages the roller |36 of thelimit switch |35, the limit switch is closed, after which continuousmovement of the table through either the dog |3| or the dog |32 servesthrough the roller |36 to shift the lever |30 into its reverse positionto reverse the position of the control valve 50 and thereby change thedirection of ow of uid to the cylinder 35.so as to start the tabletraversing in the reverse direction. The switch |35 is connected byflexible BX conduits |3'l with an adjustable electrical time delay relay|38 and is connected by the wires |30 and |60 with the solenoid |00 onthe r the operator.

It is desirable to control the opening valve |03. When the table dogsrock the roller |36 in either direction to close the limit switch |35,it closes a circuit to set the time delay relay V|38 in motion and alsoserves simultaneously to energize the solenoid |043 to open the valve|03, which allows fluid under pressure to exhaust from the feed motor90. No fluid will flow into the feed motor 90, however, until thereversing mechanism has shifted a sufficient distance so that the valvepiston il of the valve 'ifi cuts 01T the l pipe t0, cutting oif theoutput of the fluid pump l from the table cylinder l0 and sluiting tothe pipe 97 to actuate the feed motor 90. The adjustable time delayrelay |38 may be set to allow the solenoid |00 to be energized for adefinite time interval, after which the solenoid |00 is deenergized andthe valve |03 automatically closed to stop the transverse movement ofthe wheel I after a predetermined transverse feed of the grinding wheelhas been accomplished.

Hydraulic counterbalcnce An adjustable by-pass valve |05 is provided inthe pipe This valve determines the pressure applied to actuate the crossfeed movement of the wheel. This valve -is preferably set so thatsufficient fluid exhausts therethrough into a pipe |60 which is conveyedto a hydraulic counter.- balance mechanism comprising a cylinder |01having a piston M8 slidably mounted therein. The piston M3 is connectedto the lower end of the feed screw 2A. Fluid under pressure passingthrough the pipe |40 enters a cylinder chamber m9 below the piston |510and serves normally to exert a pressure on the screw 2d in an upwarddirection. This uniform pressure is applied at all times to the feedscrew so as to, in effect, counterbalance either the whole or part ofthe weight of the vertical slide and the parts carried thereby, so thatthe manually operable feed wheel 20 may be easily and readily rotatedvertically to adjust the slide without undue exertion on the part ofThis vertical pressure exerted on the feed screw 20 also serves moreaccurately to control the positioning of the slide Il as well as thewheel slide i6 and grinding wheel l5 due to the fact that the pressurebetween the screw and the nut is always in the same direction regardlessof Whether the vertical slide |'l is being moved upwardly or downwardly.The pressure within the cylinder chamber |03 may be governed by aby-pass valve |50 so that the required pressure may be obtained toproduce the desired results.

Motor driven vertical movement of wheel It is desirable to provide asuitable power operated mechanism for raising and lowering the wheel insetting up the machine for grinding work pieces of varying predeterminedsizes. This is preferably accomplished by providing a motor drive forthe shaft 2|. An electric motor |60 is mounted within the base I0. Apulley |6| mounted on the motor shaft, which is preferably of a multipleV-grooved type, is connected by means of multiple V-belts |02 with amultiple grooved pulley .|03 mounted on the rear end of the shaft 2|. Itwill be readily apparent that when the motor |00 is rotated in eitherdirection, a rotary motion will be transmitted to the shaft 2| to rotateit in either direction which,

- througliithe worm 22 and worm gear 23, willV produce a verticalmovement of the feed screw 20, the vertical slide il, as well as thegrinding wheel slide I6 and grinding wheel l5. A suitable control switch|65 is mounted on the front of the which when moved into the up positionserves toA rotate the motor in one direction so as to cause an upwardmovement of the vertical slide "I1,

. wheel slide I6 and grinding wheel I5, and when moved to a downposition serves to rotate the motor |66 in the reverse direction tocause a downward movement of the slide l1 and grinding Wheel I5. Thismotor driven mechanismvserves as a rapid positioning movement for thegrinding wheel I5 in setting up the machine, the ne adjustment of thesame being obtained by a manual manipulation of the feed wheel 26.

The operation of this improved surface grinding machine will be readilyapparent from the foregoing disclosure. Assuming all of the parts havebeen previously adjusted, a work piece is placed on the table II and thelever 66 is shifted to permit exhaust of fluid from the table system.The motor 41 being in running condition serves to force fluid underpressure through the system to reciprocate the table II- through astroke of a predetermined length as governed by the adjustablev tabledogs |3| and |32. At the end of the stroke in either direction, when thedog |3I or the dog |32 nengages the roller |36 of the reversing lever|36, the roller |36 rst rocks relative to the lever v|36 to close thelimit switch |35,

therebystarting the time delay relay |38 in operation andlsimultaneously energizing the solenoid |64 so` that the exhaust pipeline from the feed motor 96 is opened. Continued movement of eithertable dog |36 or |32 shifts the reversing valve 56 into a reverse.position and at the same time, through the lever 82, shifts the valve|14 to cut oil' the fluid motor 16 from the table cylinder 35 andtransfers this uid under pressure from the pumpv 16 to index or feed thegrinding wheel slide I6 and the grinding wheel I5 transversely duringthe time interval when the reverse valve is shifting to change the'direction of movement of the table I I. By manipulation of the timerelay |38, the extent of cross feed of the grinding wheel may be variedas desired. During all of this movement of the machine, bothreciprocationof the table during grinding and the transverse feedingmovement of the wheel at reversal, a uniform pressure is maintainedwithin the hydraulic counterbalance cylinder 35 and the lever 62 alsoshifts to move.

the valve stem 15 of the valve 14 toward the right to'cut off the pipe13 so that valve piston 14 cuts off the pipes 13 and 66 so that all thefluid under pressure from the pump 16 is conveyed to the wheeltraversing or feeding motor 66. When the valve 14 shifts to its extremerighthand position, a valve chamber |5| located between the valvepistons 16 and 11 again connects the pipe 13 with the pipe 66 .so thatsubstantially the entire volume of iiuid from the pump 16 is conveyed tothe table cylinder to assist tl'ie -pump 46 in traversing the table'IIat a rapid rate. In all positions of the valve `above described, therevis suicient fluid escaping through the by-pass valve |45 to facilitateobtaining the desired fluid pressure within the chamber |49 of thehydraulic counterbalan'ce Y cylinder |411 It will be readily apparentfrom the foregoing disclosure that the upper pump 46 of the tandem pumpis utilized to traverse the table I exclusively, whereas fluid from thelower pump 16 of the tandem pump is utilized to maintain a. pressure atall times within the counterbalance cylinder chamber |49 and during thenormal table traverse to supplement the pressure from the pump 46 toreciprocate the table at a rapid rate and also during the period ofreversal serves to actuate the fluid motor 96 to cause a transversefeeding movement of the wheel slide I6 and grinding wheel I5.

It will thus be seen that there has been provided by this inventionapparatus in which the various objects hereinbefore set forth togetherwith many thoroughly practical advantages are successfully achieved. Asmany possible embodiments may be made of the above invention and as manychanges might be made in the embodiment above set forth, it is to beunderstood that all matter hereinbefore set forth or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

1. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a longitudinally reciprocable worksupporting table, a separatefuid motor for said slide and table, aseparate control valve for each of said motors, a `uid pressure systemincluding two motor driven pumps, operative connections. between one ofsaid pumps and said table valve and motor to reciprocate the table, andoperative connections between said second pump and said slide motor andvalve to feed the wheel transversely at the end of the table stroke,said lat-` ter connections being arranged to connect the second pumpwith said table valve and cylinder during the normal reciprocatorymovement of the table to supplement said first pump.

2. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a longitudinally reciprocabletable, a separate fluid motor for said slide and table, a

separate control valve for each of said motors, a

fluid pressure system including two motor driven fluid pumps, operativeconnections between one of said pumps and the table valve and cylinderto reciprocate the table, and means alternately to connect said secondpump to said wheel slide motor during the table reversal period and tosaid table valve and cylinder during the normal reciprocatoryvmovementof said table.

3. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a longitudinally reciprocabletable, a separate fluid motor for said slide and table, 'a separatecontrol valve for each of said motors, a uid pressure system includingtwo motor driven fluid pumps, operative connections between one of saidpumps and said table valve and cylinder to reciprocate the table, andoperative connections alternately to connect said second pump tothewheel slide valve and motor to feed the grinding wheel transversely atthe end of the table stroke and to connect said second motor to saidtable valve and cylinder during the normal grinding stroke of saidtable.

4. Ina surface grinding machine, a rotatable grinding wheel, atransversely movable Wheel slide therefor, a vertically movable slidefor said transverse slide, hydraulic counterbalance .for said verticalslide including a piston and cylinder, a longitudinally reciprocabletable, a separate uid motor for said'wheel slide and table, a separatecontrol valve for each of said motors, a fluid pressure system includingtwo motor driven pumps, operative connections between one of said pumpsand said table valve and cylinder to reciprocate said table, operativeconnections bctween said second pump alternately to connect said secondpump to the wheel slide valve and 'motor to feed the Wheel transverselyat the end' of the table stroke and to connect said second pump to saidtable valve and cylinder during the normal grinding stroke thereof, andoperative connections between said second pump to maintain a uniformpressure in said counterbalance cylinder at all times.

5. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a longitudinally reciprocabletable, means including a reversing lever to reciprocate said table, afluid pressure piston and cylinder operatively connected to traversesaid slide,' a control valve to control the admission to and exhaust offluid from said cylinder, a solenoid valve to control the exhaust offluid from said valve and cylinder which is normally closed duringreciprocation of said table, a limit switch on said reverse lever, dogson said table to engage said limit switch to actuate the same and toshift the reversing lever, and an electrical time delay relay which isrendered operative when the reverse lever is shifted to energize saidsolenoid valve to permit exhaust of fluid from the slide cylinder andthereby cause a transverse traversing of the grinding wheel during thetable reversal.

6. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a longitudinally reciprocabletable, means including a reversing lever to reciprocate y said table, afluid pressure piston and cylinder operatively connected to traversesaid slide, a control valve to control the admission to and exhaust offluid from said cylinder, a solenoid valve to control the exhaust offluid from said valve and cylinder which is normally closed duringreciprocation of said table, a limit switch actuated vin timed relationwith said reverse lever, dogs on said table to shift the reversinglever, and an electrical time delay relay which is rendered operativewhen the reverse lever is shifted to energize said solenoid valve topermit exhaust of fluid from the slide cylinder and thereby cause atransverse traversing of the grinding wheel during the table reversal.

7. In a surface grinding machine, a rotatable grinding wheel, atransversely movable slide therefor, a vertical slide to support saidtransverse slide, a longitudinally reciprocable work supporting table,means including a manually operable nut and screw mechanism to feed saidvertical slide in either direction to cause the grinding wheel toapproach or recede from said work table, means including a reversibleelectric motor to actuate said nut and screw mechanism including apiston and cylinder operatively connected to the end of said screw,means to supply fluid under pressure to said cylinder, said pressurebeing sufficient to take up the backlash between the nut and screw andto assure the thrust between the screw and nut is always in the samedirection regardless of whether the screw and nut are operated to movethe slide up or down.

8. In a surface grinding machine, a rotatable grinding wheel, meansincluding a vertical slide to support said wheel, manually operablemeans including a nut and screw mechanism to adjust the position of saidslide and wheel in a vertical direction, means including a reversibleelectric motor to operate said nut and screw in either direction tocause an up or down movement of said slide and wheel, and a fluidpressure end thrust mechanism for said screw including a pis ton andcylinder operatively connected to the end of said screw, means to supplyfluid under pressure to said cylinder, and means to adjust said pressureso that the screw and nut are always held in the same position relativeto each other regardless of whether the nut and screw are actuated tocause an up or down movement of the slide.

9. In a surface grinding machine, a rotatable grinding wheel, meansincluding a vertical slide to support said wheel, a manually operablefeed mechanism for said slide including a rotatable nut which is heldagainst endwise movement, a non-rotatable feed screw, connectionsbetween the upper end of said screw and said slide, means including areversible electric motor to rotate said nut in either direction, areversing switch therefor, and a fluid pressure end thrust mechanism forsaid screw including a piston and cylinder operatively connected to thelower end of said screw, means to supply fluid under pressure to saidcylinder, and means including a manually adjustable valve to maintain auniform pressure in said cylinder so that the thrust between the nut andscrew is always in the same direction.

ALBERT G. BELDEN. CARL G. FLYGARE.

